This invention relates to a flame retardant and moldable polycarbonates derived from dihydric aromatic compounds and alkali metal hydrogen sulfite.
It is known from U.S. Pat. No. 3,978,024 that homo-polycarbonates can be rendered flame retardant by sulfonation of the polycarbonates followed by neutralization of the sulfonic acid groups with alkali metal hydroxides. However, these sulfonated polycarbonates are not convenient to make and use.
It is also known from U.S. Pat. No. 4,028,297 dated 6-7-77 that alkali metal salts of sulfite, thiosulfate, dithionite and pyrosulfite are useful fire retardant additives for polycarbonate resin. However, these compounds are not as efficient as the present alkali metal hydrogen sulfites.